1. Field of the invention
The present invention relates to an electric power steering apparatus for a vehicle and a method of assembling the same, and more particularly to an electric power steering apparatus for a vehicle and a method of assembling the same in which an elastic member provided between a boss and a worm shaft does not suppress the movement of the worm shaft in an axial direction and a radial direction, a process of assembling a driving shaft of a motor and the worm shaft can be simplified, and the time required for assembly can be reduced.
2. Description of the Prior Art
FIG. 1 is a cross-sectional view illustrating a part of a motor and a speed reduction mechanism of the motor in a conventional electric power steering apparatus. FIG. 2 is an exploded perspective view illustrating a part of the motor and the speed reduction mechanism of the motor in the conventional electric power steering apparatus.
As illustrated in these drawings, a motor and a speed reduction mechanism of the motor in an electric power steering apparatus includes a motor 180, a driving shaft 105, an inner rotor 120, an outer rotor 115, an elastic body 110, a first bearing 150, a worm shaft 135, a worm 145, a second bearing 170, a compression screw 155, a compression spring 165, and a gear housing 160.
The motor 180 includes a driving shaft 105 extending outside a motor housing and the outer rotor 115, of which the inside is hollow, is connected with the driving shaft 105 at one end to be interlocked with the driving shaft 105.
The first bearing 150 and the second bearing 170 support the worm shaft 135 in such a manner that the worm 145 is fixed to the worm wheel 140 side where a steering shaft 130 is installed. A torsion bar is incorporated in the steering shaft 130.
The compression spring 165 supports the worm 145 toward the worm wheel 140 by being pressed against the compression screw 155 and also supports the second bearing 170. Accordingly, when the compression screw 155 is tightened, the compression screw 155 is moved to contract the compression spring 165. Consequently, the worm 145 can be firmly engaged with the worm wheel 140 by a compressive force of the compression spring 165.
The inner rotor 120 is connected to the worm shaft 135 in which the inner rotor 120 is configured to be inserted into the outer rotor 115 which is connected with the driving shaft 105 at the one end thereof.
Meanwhile, a damping coupler 210 includes the outer rotor 115, the elastic body 110, and the inner rotor 120. The damping coupler 210 interconnects the driving shaft 105 of the motor 180 and the worm shaft 135.
Here, the outer rotor 115 is configured such that the inner rotor 120 may be inserted therein, and the elastic body 110 is provided between the inner rotor 120 and the outer rotor 115.
In addition, the inner rotor 120 is formed with a hole 245 in which serrations are formed in an axial direction and connected with the worm shaft 135, which is machined with first serrations 250 opposed to the serrations of the hole 245. The outer rotor 115 having a hole (not illustrated) formed with serrations is connected with a boss 270 which includes second serrations 242 formed on the outer circumferential surface thereof in an axial direction thereof.
The boss 270 includes a hole 240 in which serrations are formed in the axial direction to be connected with the driving shaft 105 of the motor 180.
However, since the damping coupler of the conventional electric power steering apparatus as described above is configured such that the driving shaft of the motor and the outer rotor are serration-engaged with each other and the worm shaft and the inner rotor are serration-engaged with each other, it is necessary to align the serrations when coupling the damping coupler to the driving shaft and the worm shaft so as to assemble the damping coupler. Accordingly, assemblability is poor and increases the time required for assembly.
In addition, the elastic body provided between the outer rotor and the inner rotor rather suppresses the movement of the worm shaft in the radial direction, which deteriorates a clearance compensating function of the damping coupler.